This study will be directed towards elucidating the mechanism of CNS cell death during ischemia and towards seeking means to extend the period of ischemia compatible with recovery. The initial experiments will attempt to determine which of the many changes that occur following complete stasis of circulation are primarily responsible for irreversible damage. These will be performed in vitro, using isolated rabbit retina as the prototype of brain, in order to control more effectively the conditions of the ischemic insult. The extent of the ischemic damage, and the degree of recovery from it, will be assessed by electronmicroscopy and by measuring rates of protein synthesis. The effect of various types and periods of ischemia on protein breakdown will be assessed.